A rude, passive-aggressive amendment, usually found at the end of a imperative sentence, that lets someone know that they will do as you ask. This will typically be learned by administrators, and mangers, working among subordinates or anyone they disdain, because being polite is HR appropriate, but it must be understood that they are peasants. It is implied that while the request is voluntary (i.e. please), the result can be assumed (i.e. thank you), because a peasant has no choice.

*This is especially common in the industry (e.g. restaurants, hotels, retail, etc).

Saying or writing "Please and thank you" at the end of a request can be a sensible shorthand between an aging parent and a loving son, daughter or grandchild. The more old people depend on the busy young, the more important it is for the elderly not to waste time with extended exchanges so 'please and thank you' is an assumption, based on previous familial knowledge, that a simple request will be carried out without requiring a reply.